I've got 2 pressurized systems (CO2 tank, regulator, etc), and I've also got the Hagan DIY CO2 kit.
As long as you aren't keeping really sensitive fish/shrimp, the DIY method works pretty well. I decided to buy the kit instead of doing it with pop bottles, because the I didn't want to mess with drilling holes in pop bottles and mucking about with silicone. Plus it looks nicer. I did swap out the Hagan CO2 ladder with a $10 diffuser.
Using store bought yeast, it runs pretty consistently for about 2 weeks, then you just dump it out and refill. Its done wonders for my tank that's heavily planted with low light plants (mostly types of java fern and moss).